Interpretive Summary: Polyphenols from cinnamon have been described recently as insulin sensitizers and antioxidants but their effects on onset of the metabolic syndrome have not been documented. The aim of this study was to determine the effects of cinnamon on insulin resistance and body composition, using an animal model of the metabolic syndrome, the high-fat/high-fructose fed rat. The metabolic syndrome is often an early stage of type 2 types in which insulin becomes inefficient followed by higher levels of insulin production by the pancreas that ultimately leads to type 2 diabetes. More than 60 million people in the U.S. have the metabolic syndrome and more than 25 million people decline from the metabolic syndrome to type 2 diabetes. In this study, rats fed a diet high in fat and the refined sugar fructose (high in sweetened beverages) developed signs and symptoms of the metabolic syndrome. Addition of cinnamon to the diet of these rats prevented the onset of the risk factors associated with the metabolic syndrome. The high-fat/high-fructose diet also induced a reduction in pancreas weight that was prevented by the addition of cinnamon to the diet. There was an accumulation of fat in rats consuming the diet high in sugar and fat that was alleviated by the cinnamon. In summary, these results demonstrate that in animals fed a high-fat/high-fructose diet to induce insulin resistance, cinnamon alters body composition in association with improving insulin sensitivity. These data should be of interest to scientists, medical personnel, and the lay public.

Technical Abstract: Polyphenols from cinnamon (CN) have been described recently as insulin sensitizers and antioxidants, but their effects on the glucose/insulin system in vivo have not been totally investigated. The aim of this study was to determine the effects of CN on insulin resistance and body composition, using an animal model of the metabolic syndrome, the high-fat/high-fructose (HF/HFr) fed rat. Four groups of 22 male Wistar rats were fed for 12 weeks with: (i)(HF/HFr) diet to induce insulin resistance, (ii) HF/HFr diet containing 20 g cinnamon/kg of diet (HF/HFr+CN), (iii) Control diet (C), (iv) Control diet containing 20 g cinnamon/kg of diet (C+CN). Data from hyperinsulinemic euglycemic clamps showed a significant decrease of the glucose infusion rates in rats fed the HF/HFr diet. Addition of CN to the HF/HFr diet increased the glucose infusion rates to those of the control rats. The HF/HFr diet induced a reduction in pancreas weight which was prevented in HF/HFr+CN group (p<0.01). Mesenteric white fat accumulation was observed in HF/HFr rats vs. control rats (p<0.01). This deleterious effect was alleviated when CN was added to the diet. In summary, these results suggest that in animals fed a HF/HFr diet to induce insulin resistance, CN alters composition in association with improved insulin sensitivity.